1. Field of the Invention
The present invention relates to a zoom lens used in a silver-halide camera, a digital camera, a video camera or the like.
2. Description of the Related Art
Conventionally, in a zoom lens used in a silver-halide camera, a digital camera, a video camera or the like, it is known as a method for focusing from an object at the infinite distance to an object at a near distance to shift whole or a part of one unit out of lens units that change mutual spaces during a zooming operation (For example, refer to Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 3-289612 or Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 3-228008).
There is a type including four units having positive-negative-negative-positive power arrangement in order from the object side and performing focusing by shifting the positive first lens unit toward the object side, as in the method shown in KOKAI No. Hei 3-289612. Also, there is another type including three lens units having positive-negative-positive power arrangement in order from the object side and performing focusing by shifting forth the negative second lens unit toward the object side as in the method shown in KOKAI No. Hei 3-228008.